Question

Explain the functional roles of the A, P, and E sites during translation.

Short answer

The A site on the ribosome reads mRNA codons and hosts charged tRNA molecules, the P site is where the growing peptide chain is formed, and the E site is where uncharged tRNA molecules exit the ribosome.

Step-by-step solution

Aminoacyl (A) Site

During the initiation of translation, the A site hosts incoming charged tRNA molecules (ones carrying amino acids). These tRNA molecules carry an anticodon that matches the codon on the mRNA strand. The A site is where the ribosome reads the mRNA codons.

Peptidyl (P) Site

The P site is the location on the ribosome where the tRNA holding the growing peptide chain resides. Once the codon on the mRNA is recognized by the corresponding anticodon on the tRNA at the A site, a peptide bond is formed between the new amino acid brought by tRNA to the A site, and the growing chain at the P site tRNA.

Exit (E) Site

The E site is where deacylated tRNA (ones that have lost their amino acid) exit the ribosome. After the peptide bond formation at the P site, the tRNA molecule at the P site, now uncharged, moves to the E site and is subsequently released.